Coastal changes

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  • Created by: Holly45
  • Created on: 28-03-15 11:29

Defences

SEA WALL:

  • look ugly
  • restricts access to the beach
  • large waves can undermine them
  • very strong and long lasting
  • land and buildings awe protected

WOODEN GROYNES:

  • prevent LSD
  • need to be maintained
  • may only last 10 years
  • restricts access along the beach
  • displaces wave energy

RIP- RAP:

  • absorbs wave energy
  • reduces erosive powers
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How coastal erosion can be managed

  • covered by Shoreline Management Plans (SMP'S)
  • advance the coastline: move the coastline seaward with land reclamation (expensive)
  • hold the line: keep the coastline in the same place, using hard and soft engineering (expensive)
  • strategic retreat: allow the coastline to move inland, allowing some erosion but defending when nessisary (cheaper)
  • doing nothing: allow natural erosion and flooding to take place (lowest cost option)
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Climate change on coasts

  • by 2100, sea levels could be 50-100cm higher
  • the UK may get more powerful winter storms and frequent rainfall
  • increased rates of erosion on cliff faces, and more frequent mass movement
  • deposition on spits and sand dunes
  • flooding of low coastal areas
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Weathering, mass movement and sea level rise

  • freeze thaw is a type of mechanical weathering (water enters cracks in the rock, freezes, expands and splits it apart
  • chemical weathering occurs when water reacts with minerals in a rock. It dissolves the calcite in limestone, or react by hydrolysis with feldspar in granite
  • during heavy rainfall, cliffs often become saturated with water and water flowing inside makes the cliff weak
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Contrasting coasts

HARD ROCK COAST:

  • cliffs tend to be high and vertical
  • beaches made up of pebbles and bolders
  • landforms such as caves, arches and stacks
  • wave cut platforms

SOFT ROCK COASTS:

  • cliffs are low and gently sloping
  • beaches of sand or mud
  • no stacks or stumps
  • wave cut platforms are unusual
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Coast erosion

HYDRAULIC ACTION:

  • the force of water striking cliffs and forces air into joints and faults which fracture the rock

ABRASION:

  • rock and sand thrown with force against cliffs causing the cliffs to wear away

ATTRITION:

  • the rocks thrown against cliffs causing the rocks to be broken up
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Concordant and discordant coasts

CONCORDANT:

  • parallel to the coast
  • same type of rock all along the length
  • tend to have fewer bays and headlands
  • Lulworth Cove

DISCORDANT:

  • alternate hard and soft rock
  • the soft rock erodes quicker than the hard rock
  • Swanage Bay
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Waves and landforms

DESTRUCTIVE WAVES:

  • break with a steep descent with little swash so backwash is strong and erodes material
  • plunging waves are close together and can form rip currents which remove sand and create steeper beaches

CONSTRUCTIVE WAVES:

  • spill up the beach quite strongly and travel long distances
  • the water soaks up into the beach so the returning water is weaker
  • the waves tend to move sand and other materials up the beach to the land
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How LSD forms landforms

  • material is moved along the coast
  • if there is a change of direction in the coastline this material is deposited across the bay or river mouth
  • the bay may eventually be closed off as the sand bar reaches the other side
  • the depositation will end when the current becomes too strong from a river
  • a spit will form and behind it salt marches form
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